The present invention pertains to a new and improved method and apparatus for determining the location of an individual within a specified area. More particularly, this invention relates to an apparatus which comprises the combination of a portable device which, in conjunction with a series of fixed transmitters, provides information which may be processed by a monitoring station to determine the location of a user carrying the portable device.
There are numerous workplace situations where it is advantageous or essential for individuals to have a means of communicating to a monitoring station that they are in an emergency situation and simultaneously allowing their location to be determined. For example, in a correctional facility an officer may be unable to verbally communicate his location during an emergency. In addition, there are situations when it may be desirable to transmit one""s location in a silent, non-obtrusive manner, either as a means of reporting a particular event or situation, or merely to allow a surveillance office to be apprised of the user""s location.
There are two general types of personal alarm monitoring (PAM) systems for monitoring the location of a person. In a passive PAM system, a user simply follows a pre-arranged schedule. The monitoring station assumes the location of the user based upon the schedule. However, if a user travels to a location other than his assigned location, or alters the schedule, the user""s location is unknown and cannot be determined by the monitoring station.
In contrast, active PAM systems determine the location of the user when requested or required through a communication system with the user. Although there are numerous active PAM systems utilizing a variety of technologies, including infrared, ultrasonic, and radio frequency systems, such conventional systems are often unable to reliably determine the location of a user. Radio frequency schemes can report wrong locations due to the inability of such systems to properly account for attenuation or multiple reflections or receptions of the radio frequency signals. Infrared and ultrasonic locating systems are often ineffective due to interference problems caused by smoke or noise, and may suffer from directionality limitations. Such installations are also usually expensive, since the sensors or receivers are typically hand-wired to the monitoring station.
It is thus an object of the present invention to provide an improved system for monitoring the location of an individual in a building or other defined area.
It is a further object of the present invention to provide a method and apparatus for determining the location of an individual with precision and accuracy.
Another object of the present invention is to provide a system which is simple and inexpensive to install and operate, and which can function in a defined area having hallways, rooms and open areas.
It is yet another object of the present invention to provide a system which allows for economical expansion of the range of coverage and/which exhibits improved precision over conventional systems.
Still a further object of the present invention is to provide a method and apparatus for location determination which utilizes a series of fixed transmitters located throughout the area to be monitored and portable transceivers which are carried by the individuals whose whereabouts are to be monitored.
A personal alarm monitor system in accordance with the present invention utilizes radio frequency identification (RFID) tag transmitters positioned throughout a building or other specified area or premises; one or more portable personal alarm monitor transceivers or xe2x80x9cbody unitsxe2x80x9d; and a monitoring station. A body unit is carried by a user whose location is desired to be monitored. The RFID tags are installed throughout the premises at fixed locations; each is provided with a unique identification code. The identification codes and corresponding locations for the RFID tag units are known by the monitoring station.
The RFID tags broadcast low-level identification radio signals, preferably on an intermittent basis. Each body unit is capable of receiving the signals from all RFID tags. As a body unit wearer travels through the premises, the body unit receives identification data from each RFID tag it passes. The identification data is stored by the body unit. The most-recently received data is indicative of the current location of the body unit and its wearer. The collection of identification data stored by the body unit provides a history of the wearer""s path of travel. The stored identification data can be downloaded or transmitted by the body unit to the monitoring station to provide location information to supervisory personnel.
The RFID tags are located throughout the premises as appropriate to provide useful location data. Even though the tags are low-power devices, and may include antenna structures to direct the broadcasts in particular directions, there exists the possibility that a body unit will receive identification data from RFID tags which are not directly along the wearer""s path of travel. Accordingly, the invention embodies logic, enabled by a microprocessor in the body unit, to process the signals received by the body unit, the logic allowing rejection of signals from RFID tags which would not logically correspond to a path of travel dictated and permitted by the geometry and layout of the premises. The logic also allows compensation to be made for defective or inoperative RFID tags. Only when a received identification signal is verified is it passed to a list which serves as the travel history for the body unit and its wearer and can be transmitted to the monitoring station for use in determining the current location of the body unit/user as well as its path of travel.
The positioning of RFID tags, and the identification scheme associated therewith, interfaces with the processing logic. In a particular embodiment of the invention, the placement of RFID tags include the placement of paired tags at portals or gateways, such as doorways, linking defined designated areas of the premises to be monitored. The identification data associated with each such gateway RFID tag identifies it as a gateway tag and allows its complementary tag to be identified, as well as identifying its location in the monitored premises.
The identification data transmitted by a gateway tag allows a body unit receiving the data to identify its linked complement gateway tag; the processing logic recognizes that sequential reception of signals from both linked tags is required for a valid passage through the referenced gateway or portal between defined areas. Similarly, as all RFID tags in an defined area are logically linked through their identification codes, body unit processing logic can reject a received RFID tag broadcast if it corresponds to a location in an area which has not been previously entered by a previously recorded passage through a gateway as reflected by previous receipt of identification data from the associated pair of gateway tags.